1. Field of the Invention
This invention relates generally to methods and machinery used to fabricate cellular materials, particularly those cellular materials used in window coverings.
2. Description of the Prior Art
Cellular window coverings are well known in the art. These products have a series of interconnected cells usually made from fabric material. Typically, these products are made by folding and gluing sheets or strips of material to create a cellular structure or by connecting a series of webs between two parallel sheets.
One type of cellular window covering is constructed by folding over the edges of flat sheets of material and gluing the free edges to form a cell, or multi-cellular structure, and then stacking and gluing the cells on top of each other to form the cellular window covering. The cells can then be cut to the width of the window in which it will be installed. Related U.S. Pat. Nos. 4,631,108 and 4,450,027 to Colson discloses a method and apparatus for fabricating expandable honeycomb insulation panels from a continuous length of thin plastic film. The film is folded into a tubular structure by folding opposite lateral edges of the film onto one side. An adhesive is applied to at least one side of this structure. Then the tubular structure is continuously wrapped around a rotating arm under constant tension in an effective, uniform manner that eliminates internal stresses that could otherwise cause warps or wrinkles. The tubular structure is continuously stacked in layers on a flat surface or a plurality of flat surfaces to eliminate any curves that might cause wrinkles or warps in the finished product. The apparatus includes an initial creaser assembly in which a pair of spaced-apart sharp wheels are pressed into the film to form uniform creases where the film material will be folded. It also includes a folding assembly to fold the lateral edges at the crease over the mid-portion thereof and a press assembly to mechanically crimp the folds. The apparatus contains a heat setting assembly for heating the plastic film material to a sufficiently high temperature so that it looses its elasticity and becomes sufficiently plastic to permanently set the folds therein. A drive assembly pulls the plastic film through the folding and heat setting assemblies, and a positive displacement pump feeds a liquid adhesive through an applicator for deposition onto the surface of the folded tubular plastic film. The pump is driven from the film drive assembly so that the rate of deposition of the adhesive material on the film is always in direct relation to the rate of speed in which the film moves through the apparatus in order to maintain uniform beads of adhesive for clean cut glue lines in the finished panel product. The apparatus also includes a rotatable stacking arm having two spaced apart flat surfaces connected by curved ends. A tension and speed control assembly maintains a constant tension of the film as it is stacked uniformly in layers on the rotating arm or stacking bed. After a sufficient amount of film is wrapped around the arm cuts are made through the stack to remove from the arm the cellular structure that has been formed.
A significant shortcoming of the method and apparatus disclosed by Colson is that only the cellular material that has been formed on the flat surfaces can be used for window covering products. This is so because the cells in the material stacked on the curved ends of the arm retain some of their curvature. If this material were attached to a headrail and hung in front of a window the curves in the cells would be quite noticeable and unattractive. Nevertheless, the process and machine disclosed by Colson continues to be used commercially. Those users simply scrap the material that is cut from the curved ends of the arm. It is quite common for 15% to 20% of the starting material cut from the ends of the rotating arm to be and scrapped in this process. Additional waste results from another limitation of this process. The stacks of material cut from the flat surfaces of the arm have a width not greater than the length of each flat surface. The height of the stack is limited by the distance between the ends of the arm and the factory floor when that end is at its lowest position. After the stacks are removed from the rotating arm they must be cut to provide a panel of cellular material having a width and length equal to the size of the shade being made. Often two or more panels can be cut from each stack. Yet, seldom is the entire stack used to make the desired panels. Twenty to twenty-five percent of a stack can be excess material that is scrapped. Consequently, 35% to 45% of the starting material used in the process and machine disclosed by Colson is wasted.
Another method and apparatus for malting cellular products is disclosed by Rasmussen in U.S. Pat. No. 3,963,549. In this method material is wound around two spaced apart drums. Lines of an adhesive are applied to the material prior to being wound. As a result overlaying surfaces of the material are bonded together at the glue lines forming a cellular structure. After a desired amount of material has been collected the material is cut and removed from the apparatus. The results are similar to that produced by Colson. The structure created on the drums is curved and cannot be used for window covering products.
Another method for manufacturing honeycomb materials in which a continuous length of material is wrapped on a wheel is disclosed by Schnebly in U.S. Pat. No. 4,732,630. The continuous length of material is folded along opposite side portions thereof into a generally flat tubular form. Adhesive is then applied along the length of the continuous material by first heating the material, applying the adhesive in a liquid state to the heated material, and then cooling the material to solidify the adhesive. The folded tubular material with solidified adhesive lines thereon is then wound about a rack in such a manner that the tubular material is deposited in a plurality of continuous layers one on another with the lines of adhesive being disposed between adjacent layers. The wound layers are then radially cut and placed in a vertically aligned stack while they are removed from the rack. The vertically stacked layers are then heated to a temperature sufficient to activate the lines of adhesive and bond the layers together. Finally, the stacked tubular material is cooled to form a unitary stack of tubular, expandable honeycomb material. This process is time consuming and expensive because the material and adhesive must be heated twice. Another problem is that the material and adhesive expand and contract at different rates. Consequently, the cellular structure will be wrinkled with the amount of wrinkles being dependent upon the materials used and the placement of the adhesive. Less wrinkling will occur if the cells are symmetrical and the adhesive is along a longititudinal centerline of the cells. The process is not practical for making a tabbed cell.
A principal advantage of the methods and apparatus disclosed by Colson, Rasmussen and Schnebly is their production capacity. The machines can be operated at relatively high speeds such that the material is being wound at speeds of 500 to 1000 feet per minute. Thus, there is a need for a machine that can rapidly produce cellular products from tubular structures without high scrap rates. The process should be able to produce wrinkle-free cellular structures of all types of cells.